New progresses on cell surface protein HSPA5/BiP/GRP78 in cancers and COVID-19.

Heat-shock-protein family A (Hsp70) member 5 (HSPA5), aliases GRP78 or BiP, is a protein encoded with 654 amino acids by the HSPA5 gene located on human chromosome 9q33.3. When the endoplasmic reticulum (ER) was stressed, HSPA5 translocated to the cell surface, the mitochondria, and the nucleus complexed with other proteins to execute its functions. On the cell surface, HSPA5/BiP/GRP78 can play diverse functional roles in cell viability, proliferation, apoptosis, attachments, and innate and adaptive immunity regulations, which lead to various diseases, including cancers and coronavirus disease 2019 (COVID-19). COVID-19 is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, which caused the pandemic since the first outbreak in late December 2019. HSPA5, highly expressed in the malignant tumors, likely plays a critical role in SARS-CoV-2 invasion/attack in cancer patients via tumor tissues. In the current study, we review the newest research progresses on cell surface protein HSPA5 expressions, functions, and mechanisms for cancers and SARS-CoV-2 invasion. The therapeutic and prognostic significances and prospects in cancers and COVID-19 disease by targeting HSPA5 are also discussed. Targeting HSPA5 expression by natural products may imply the significance in clinical for both anti-COVID-19 and anti-cancers in the future.

Differentially Expressed Genes in Dental Pulp Tissues of Individuals With Symptomatic Irreversible Pulpitis With and Without History of COVID-19.

INTRODUCTION: Increased levels of proinflammatory markers have been reported in tissues of individuals with Coronavirus Disease 2019 (COVID-19). We hypothesize that inflamed dental pulp tissues of individuals with previous history of COVID-19 may present a differential inflammatory gene expression profile in comparison with individuals who never had COVID-19. MATERIALS AND METHODS: Dental pulp tissues were collected from 27 individuals referred for endodontic treatment due to symptomatic irreversible pulpitis. Of these, 16 individuals had a history of COVID-19 (6 months to 1 year post infection) and 11 individuals had no previous history of COVID-19 (controls). Total RNA from pulp tissue samples was extracted and subjected to RNA sequencing for comparison of differentially expressed genes (DEGs) among groups. DEGs showing log2(fold change) > 1 or < -1, and P < .05 were considered significantly dysregulated. RESULTS: RNA sequencing identified 1461 genes as differentially expressed among the groups. Of these, 311 were protein coding genes, 252 (81%) that were upregulated and 59 (19%) that were downregulated in the COVID group compared with controls. The top upregulated genes in the COVID group were HSFX1 (4.12-fold change) and LINGO3 (2.06-fold change); significantly downregulated genes were LYZ (-1.52-fold change), CCL15 and IL8 (-1.45-fold change). CONCLUSIONS: Differential gene expression in dental pulp tissues of COVID and non-COVID groups suggests potential contribution of COVID-19 on dysregulating inflammatory gene expression in the inflamed dental pulp.

Leukocyte surface expression of the endoplasmic reticulum chaperone GRP78 is increased in severe COVID-19.

Hyperinflammation present in individuals with severe COVID-19 has been associated with an exacerbated cytokine production and hyperactivated immune cells. Endoplasmic reticulum stress leading to the unfolded protein response has been recently reported as an active player in inducing inflammatory responses. Once unfolded protein response is activated, GRP78, an endoplasmic reticulum-resident chaperone, is translocated to the cell surface (sGRP78), where it is considered a cell stress marker; however, its presence has not been evaluated in immune cells during disease. Here we assessed the presence of sGRP78 on different cell subsets in blood samples from severe or convalescent COVID-19 patients. The frequency of CD45+sGRP78+ cells was higher in patients with the disease compared to convalescent patients. The latter showed similar frequencies to healthy controls. In patients with COVID-19, the lymphoid compartment showed the highest presence of sGRP78+ cells versus the myeloid compartment. CCL2, TNF-α, C-reactive protein, and international normalized ratio measurements showed a positive correlation with the frequency of CD45+sGRP78+ cells. Finally, gene expression microarray data showed that activated T and B cells increased the expression of GRP78, and peripheral blood mononuclear cells from healthy donors acquired sGRP78 upon activation with ionomycin and PMA. Thus, our data highlight the association of sGRP78 on immune cells in patients with severe COVID-19.

Collagen-Specific HSP47+ Myofibroblasts and CD163+ Macrophages Identify Profibrotic Phenotypes in Deceased Hearts With SARS-CoV-2 Infections.

Background Cardiac fibrosis complicates SARS-CoV-2 infections and has been linked to arrhythmic complications in survivors. Accordingly, we sought evidence of increased HSP47 (heat shock protein 47), a stress-inducible chaperone protein that regulates biosynthesis and secretion of procollagen in heart tissue, with the goal of elucidating molecular mechanisms underlying cardiac fibrosis in subjects with this viral infection. Methods and Results Using human autopsy tissue, immunofluorescence, and immunohistochemistry, we quantified Hsp47+ cells and collagen α 1(l) in hearts from people with SARS-CoV-2 infections. Because macrophages are also linked to inflammation, we measured CD163+ cells in the same tissues. We observed irregular groups of spindle-shaped HSP47+ and CD163+ cells as well as increased collagen α 1(I) deposition, each proximate to one another in "hot spots" of ≈40% of hearts after SARS-CoV-2 infection (HSP47+ P<0.05 versus nonfibrotics and P<0.001 versus controls). Because HSP47+ cells are consistent with myofibroblasts, subjects with hot spots are termed "profibrotic." The remaining 60% of subjects dying with COVID-19 without hot spots are referred to as "nonfibrotic." No control subject exhibited hot spots. Conclusions Colocalization of myofibroblasts, M2(CD163+) macrophages, and collagen α 1(l) may be the first evidence of a COVID-19-related "profibrotic phenotype" in human hearts in situ. The potential public health and diagnostic implications of these observations require follow-up to further define mechanisms of viral-mediated cardiac fibrosis.

Regulatory role of endoplasmic reticulum resident chaperone protein ERp29 in anti-murine ß-coronavirus host cell response.

Gap junctional intercellular communication (GJIC) involving astrocytes is important for proper CNS homeostasis. As determined in our previous studies, trafficking of the predominant astrocyte GJ protein, Connexin43 (Cx43), is disrupted in response to infection with a neurotropic murine ß-coronavirus (MHV-A59). However, how host factors are involved in Cx43 trafficking and the infection response is not clear. Here, we show that Cx43 retention due to MHV-A59 infection was associated with increased ER stress and reduced expression of chaperone protein ERp29. Treatment of MHV-A59-infected astrocytes with the chemical chaperone 4-sodium phenylbutyrate increased ERp29 expression, rescued Cx43 transport to the cell surface, increased GJIC, and reduced ER stress. We obtained similar results using an astrocytoma cell line (delayed brain tumor) upon MHV-A59 infection. Critically, delayed brain tumor cells transfected to express exogenous ERp29 were less susceptible to MHV-A59 infection and showed increased Cx43-mediated GJIC. Treatment with Cx43 mimetic peptides inhibited GJIC and increased viral susceptibility, demonstrating a role for intercellular communication in reducing MHV-A59 infectivity. Taken together, these results support a therapeutically targetable ERp29-dependent mechanism where ß-coronavirus infectivity is modulated by reducing ER stress and rescuing Cx43 trafficking and function.

The Network of Interactions between the Porcine Epidemic Diarrhea Virus Nucleocapsid and Host Cellular Proteins.

Host-virus protein interactions are critical for intracellular viral propagation. Understanding the interactions between cellular and viral proteins may help us develop new antiviral strategies. Porcine epidemic diarrhea virus (PEDV) is a highly contagious coronavirus that causes severe damage to the global swine industry. Here, we employed co-immunoprecipitation and liquid chromatography-mass spectrometry to characterize 426 unique PEDV nucleocapsid (N) protein-binding proteins in infected Vero cells. A protein-protein interaction network (PPI) was created, and gene ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) database analyses revealed that the PEDV N-bound proteins belong to different cellular pathways, such as nucleic acid binding, ribonucleoprotein complex binding, RNA methyltransferase, and polymerase activities. Interactions of the PEDV N protein with 11 putative proteins: tripartite motif containing 21, DEAD-box RNA helicase 24, G3BP stress granule assembly factor 1, heat shock protein family A member 8, heat shock protein 90 alpha family class B member 1, YTH domain containing 1, nucleolin, Y-box binding protein 1, vimentin, heterogeneous nuclear ribonucleoprotein A2/B1, and karyopherin subunit alpha 1, were further confirmed by in vitro co-immunoprecipitation assay. In summary, studying an interaction network can facilitate the identification of antiviral therapeutic strategies and novel targets for PEDV infection.

Serum glucose-regulated protein 78 (GRP78) levels in COVID-19-associated mucormycosis: results of a case-control study.

BACKGROUND: In experimental models, the expression of glucose-regulated protein 78 (GRP78) in endothelial cells played a role in the pathogenesis of mucormycosis. However, the role of GRP78 in COVID-19-associated mucormycosis (CAM) has not been studied. We hypothesized that serum GRP78 levels are elevated in subjects with CAM. OBJECTIVE: To compare the serum GRP78 levels in subjects with CAM and COVID-19 controls without mucormycosis. DESIGN AND SETTING: We performed a hospital-based, case-control study between 1 April 2021 and 31 May 2021. PARTICIPANTS: We enrolled 24 subjects each of CAM and COVID-19 subjects without mucormycosis. We also measured serum GRP78 levels in ten healthy controls. EXPOSURE: The primary exposure studied was serum GRP78 concentration, estimated using a commercially available ELISA kit in stored serum samples. RESULTS: We found the mean ± standard deviation (SD) serum GRP78 levels significantly higher (p = 0.0001) among the CAM (374.3 ± 127.3 pg/mL) than the COVID-19 (246.4 ± 67.0 pg/mL) controls. The proportion of subjects with an abnormal GRP78 level (> mean [184.8 pg/mL] plus two SD [23.2 pg/mL] of GRP78 from healthy participants) was 87.5% and 45.8% in the CAM group and COVID-19 controls, respectively. Serum GRP78 level was independently associated with CAM (odds ratio 1.011; 95% confidence interval [1.002-1.019]) after adjusting for diabetes mellitus and hypoxemia during acute COVID-19. CONCLUSION: Serum GRP78 levels were significantly higher in CAM than in COVID-19 controls. Further studies are required to the role of GRP78 in the pathogenesis of CAM.

Listeria toxin promotes phosphorylation of the inflammasome adaptor ASC through Lyn and Syk to exacerbate pathogen expansion.

Inflammasome activation exacerbates infectious disease caused by pathogens such as Listeria monocytogenes, Staphylococcus aureus, and severe acute respiratory syndrome coronavirus 2. Although these pathogens activate host inflammasomes to regulate pathogen expansion, the mechanisms by which pathogen toxins contribute to inflammasome activation remain poorly understood. Here we show that activation of inflammasomes by Listeria infection is promoted by amino acid residue T223 of listeriolysin O (LLO) independently of its pore-forming activity. LLO T223 is critical for phosphorylation of the inflammasome adaptor ASC at amino acid residue Y144 through Lyn-Syk signaling, which is essential for ASC oligomerization. Notably, a Listeria mutant expressing LLO T223A is impaired in inducing ASC phosphorylation and inflammasome activation. Furthermore, the virulence of LLO T223A mutant is markedly attenuated in vivo due to impaired ability to activate the inflammasome. Our results reveal a function of a pathogen toxin that exacerbates infection by promoting phosphorylation of ASC.

Protein disulfide isomerases (PDIs) negatively regulate ebolavirus structural glycoprotein expression in the endoplasmic reticulum (ER) via the autophagy-lysosomal pathway.

Zaire ebolavirus (EBOV) causes a severe hemorrhagic fever in humans and non-human primates with high morbidity and mortality. EBOV infection is dependent on its structural glycoprotein (GP), but high levels of GP expression also trigger cell rounding, detachment, and downregulation of many surface molecules that is thought to contribute to its high pathogenicity. Thus, EBOV has evolved an RNA editing mechanism to reduce its GP expression and increase its fitness. We now report that the GP expression is also suppressed at the protein level in cells by protein disulfide isomerases (PDIs). Although PDIs promote oxidative protein folding by catalyzing correct disulfide formation in the endoplasmic reticulum (ER), PDIA3/ERp57 adversely triggered the GP misfolding by targeting GP cysteine residues and activated the unfolded protein response (UPR). Abnormally folded GP was targeted by ER-associated protein degradation (ERAD) machinery and, unexpectedly, was degraded via the macroautophagy/autophagy-lysosomal pathway, but not the proteasomal pathway. PDIA3 also decreased the GP expression from other ebolavirus species but increased the GP expression from Marburg virus (MARV), which is consistent with the observation that MARV-GP does not cause cell rounding and detachment, and MARV does not regulate its GP expression via RNA editing during infection. Furthermore, five other PDIs also had a similar inhibitory activity to EBOV-GP. Thus, PDIs negatively regulate ebolavirus glycoprotein expression, which balances the viral life cycle by maximizing their infection but minimizing their cellular effect. We suggest that ebolaviruses hijack the host protein folding and ERAD machinery to increase their fitness via reticulophagy during infection.Abbreviations: 3-MA: 3-methyladenine; 4-PBA: 4-phenylbutyrate; ACTB: ß-actin; ATF: activating transcription factor; ATG: autophagy-related; BafA1: bafilomycin A₁; BDBV: Bundibugyo ebolavirus; CALR: calreticulin; CANX: calnexin; CHX: cycloheximide; CMA: chaperone-mediated autophagy; ConA: concanamycin A; CRISPR: clusters of regularly interspaced short palindromic repeats; Cas9: CRISPR-associated protein 9; dsRNA: double-stranded RNA; EBOV: Zaire ebolavirus; EDEM: ER degradation enhancing alpha-mannosidase like protein; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; Env: envelope glycoprotein; ER: endoplasmic reticulum; ERAD: ER-associated protein degradation; ERN1/IRE1: endoplasmic reticulum to nucleus signaling 1; GP: glycoprotein; HA: hemagglutinin; HDAC6: histone deacetylase 6; HMM: high-molecular-mass; HIV-1: human immunodeficiency virus type 1; HSPA5/BiP: heat shock protein family A (Hsp70) member 5; IAV: influenza A virus; IP: immunoprecipitation; KIF: kifenesine; Lac: lactacystin; LAMP: lysosomal associated membrane protein; MAN1B1/ERManI: mannosidase alpha class 1B member 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MARV: Marburg virus; MLD: mucin-like domain; NHK/SERPINA1: alpha1-antitrypsin variant null (Hong Kong); NTZ: nitazoxanide; PDI: protein disulfide isomerase; RAVV: Ravn virus; RESTV: Reston ebolavirus; SARS-CoV: severe acute respiratory syndrome coronavirus; SBOV: Sudan ebolavirus; sGP: soluble GP; SQSTM1/p62: sequestosome 1; ssGP: small soluble GP; TAFV: Taï Forest ebolavirus; TIZ: tizoxanide; TGN: thapsigargin; TLD: TXN (thioredoxin)-like domain; Ub: ubiquitin; UPR: unfolded protein response; VLP: virus-like particle; VSV: vesicular stomatitis virus; WB: Western blotting; WT: wild-type; XBP1: X-box binding protein 1.

Morphological Alterations and Stress Protein Variations in Lung Biopsies Obtained from Autopsies of COVID-19 Subjects.

Molecular chaperones, many of which are heat shock proteins, play a role in cell stress response and regulate the immune system in various ways, such as in inflammatory/autoimmune reactions. It would be interesting to study the involvement of these molecules in the damage done to COVID-19-infected lungs. In our study, we performed a histological analysis and an immunomorphological evaluation on lung samples from subjects who succumbed to COVID-19 and subjects who died from other causes. We also assessed Hsp60 and Hsp90 distribution in lung samples to determine their location and post-translational modifications. We found histological alterations that could be considered pathognomonic for COVID-19-related lung disease. Hsp60 and Hsp90 immunopositivity was significantly higher in the COVID-19 group compared to the controls, and immunolocalization was in the plasma membrane of the endothelial cells in COVID-19 subjects. The colocalization ratios for Hsp60/3-nitrotyrosine and Hsp60/acetylate-lisine were significantly increased in the COVID-19 group compared to the control group, similar to the colocalization ratio for Hsp90/acetylate-lisine. The histological and immunohistochemical findings led us to hypothesize that Hsp60 and Hsp90 might have a role in the onset of the thromboembolic phenomena that lead to death in a limited number of subjects affected by COVID-19. Further studies on a larger number of samples obtained from autopsies would allow to confirm these data as well as discover new biomarkers useful in the battle against this disease.

Multi-level inhibition of coronavirus replication by chemical ER stress.

Coronaviruses (CoVs) are important human pathogens for which no specific treatment is available. Here, we provide evidence that pharmacological reprogramming of ER stress pathways can be exploited to suppress CoV replication. The ER stress inducer thapsigargin efficiently inhibits coronavirus (HCoV-229E, MERS-CoV, SARS-CoV-2) replication in different cell types including primary differentiated human bronchial epithelial cells, (partially) reverses the virus-induced translational shut-down, improves viability of infected cells and counteracts the CoV-mediated downregulation of IRE1α and the ER chaperone BiP. Proteome-wide analyses revealed specific pathways, protein networks and components that likely mediate the thapsigargin-induced antiviral state, including essential (HERPUD1) or novel (UBA6 and ZNF622) factors of ER quality control, and ER-associated protein degradation complexes. Additionally, thapsigargin blocks the CoV-induced selective autophagic flux involving p62/SQSTM1. The data show that thapsigargin hits several central mechanisms required for CoV replication, suggesting that this compound (or derivatives thereof) may be developed into broad-spectrum anti-CoV drugs.

Recognition through GRP78 is enhanced in the UK, South African, and Brazilian variants of SARS-CoV-2; An in silico perspective.

New SARS-CoV-2 variants emerged in the United Kingdom and South Africa in December 2020 in concomitant with the Brazillian variant in February 2021 (B.1.1.248 lineage) and currently sparking worldwide during the last few months. The new strain 501.V2 in South Africa bears three mutations in the spike receptor-binding domain (RBD); K417 N, E484K, and N501Y, while the Brazilian B.1.1.248 lineage has 12 mutations. In the current study, we simulate the complex ACE2-SARS-CoV-2 spike RBD system in which the RBD is in the wild-type and mutated isoforms. Additionally, the cell-surface Glucose Regulated Protein 78 (CS-GRP78) associated with the ACE2-SARS-CoV-2 spike RBD complex (ACE2-S RBD) is modeled at the presence of these mutant variants of the viral spike. The results showed that E484K and N501Y are critical in viral spike recognition through either ACE2 or CS-GRP78. The mutated variants (the UK, South African, and Brazilian) of the spike RBD tightly bind to GRP78 more than in the case of the wild-type RBD. These results point to the potent role of GRP78 with ACE2 in the attachment of the new variants, which could be a key for the design of inhibitors to block SARS-CoV-2 attachment and entry to the host cell.

The chaperone GRP78 is a host auxiliary factor for SARS-CoV-2 and GRP78 depleting antibody blocks viral entry and infection.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the COVID-19 global pandemic, utilizes the host receptor angiotensin-converting enzyme 2 (ACE2) for viral entry. However, other host factors might also play important roles in SARS-CoV-2 infection, providing new directions for antiviral treatments. GRP78 is a stress-inducible chaperone important for entry and infectivity for many viruses. Recent molecular docking analyses revealed putative interaction between GRP78 and the receptor-binding domain (RBD) of the SARS-CoV-2 Spike protein (SARS-2-S). Here we report that GRP78 can form a complex with SARS-2-S and ACE2 on the surface and at the perinuclear region typical of the endoplasmic reticulum in VeroE6-ACE2 cells and that the substrate-binding domain of GRP78 is critical for this interaction. In vitro binding studies further confirmed that GRP78 can directly bind to the RBD of SARS-2-S and ACE2. To investigate the role of GRP78 in this complex, we knocked down GRP78 in VeroE6-ACE2 cells. Loss of GRP78 markedly reduced cell surface ACE2 expression and led to activation of markers of the unfolded protein response. Treatment of lung epithelial cells with a humanized monoclonal antibody (hMAb159) selected for its safe clinical profile in preclinical models depleted cell surface GRP78 and reduced cell surface ACE2 expression, as well as SARS-2-S-driven viral entry and SARS-CoV-2 infection in vitro. Our data suggest that GRP78 is an important host auxiliary factor for SARS-CoV-2 entry and infection and a potential target to combat this novel pathogen and other viruses that utilize GRP78 in combination therapy.

First Virtual International Congress on Cellular and Organismal Stress Responses, November 5-6, 2020.

Members of the Cell Stress Society International (CSSI), Patricija van Oosten-Hawle (University of Leeds, UK), Mehdi Mollapour (SUNY Upstate Medical University, USA), Andrew Truman (University of North Carolina at Charlotte, USA) organized a new virtual meeting format which took place on November 5-6, 2020. The goal of this congress was to provide an international platform for scientists to exchange data and ideas among the Cell Stress and Chaperones community during the Covid-19 pandemic. Here we will highlight the summary of the meeting and acknowledge those who were honored by the CSSI.

Can SARS-CoV-2 Virus Use Multiple Receptors to Enter Host Cells?

The occurrence of the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), responsible for coronavirus disease 2019 (COVD-19), represents a catastrophic threat to global health. Protruding from the viral surface is a densely glycosylated spike (S) protein, which engages angiotensin-converting enzyme 2 (ACE2) to mediate host cell entry. However, studies have reported viral susceptibility in intra- and extrapulmonary immune and non-immune cells lacking ACE2, suggesting that the S protein may exploit additional receptors for infection. Studies have demonstrated interactions between S protein and innate immune system, including C-lectin type receptors (CLR), toll-like receptors (TLR) and neuropilin-1 (NRP1), and the non-immune receptor glucose regulated protein 78 (GRP78). Recognition of carbohydrate moieties clustered on the surface of the S protein may drive receptor-dependent internalization, accentuate severe immunopathological inflammation, and allow for systemic spread of infection, independent of ACE2. Furthermore, targeting TLRs, CLRs, and other receptors (Ezrin and dipeptidyl peptidase-4) that do not directly engage SARS-CoV-2 S protein, but may contribute to augmented anti-viral immunity and viral clearance, may represent therapeutic targets against COVID-19.

Interaction of HSPA5 (Grp78, BIP) with negatively charged phospholipid membranes via oligomerization involving the N-terminal end domain.

Heat shock proteins (HSPs) are ubiquitous polypeptides expressed in all living organisms that participate in several basic cellular processes, including protein folding, from which their denomination as molecular chaperones originated. There are several HSPs, including HSPA5, also known as 78-kDa glucose-regulated protein (GRP78) or binding immunoglobulin protein (BIP) that is an ER resident involved in the folding of polypeptides during their translocation into this compartment prior to the transition to the Golgi network. HSPA5 is detected on the surface of cells or secreted into the extracellular environment. Surface HSPA5 has been proposed to have various roles, such as receptor-mediated signal transduction, a co-receptor for soluble ligands, as well as a participant in tumor survival, proliferation, and resistance. Recently, surface HSPA5 has been reported to be a potential receptor of some viruses, including the novel SARS-CoV-2. In spite of these observations, the association of HSPA5 within the plasma membrane is still unclear. To gain information about this process, we studied the interaction of HSPA5 with liposomes made of different phospholipids. We found that HSPA5 has a high affinity for negatively charged phospholipids, such as palmitoyl-oleoyl phosphoserine (POPS) and cardiolipin (CL). The N-terminal and C-terminal domains of HSPA5 were independently capable of interacting with negatively charged phospholipids, but to a lesser extent than the full-length protein, suggesting that both domains are required for the maximum insertion into membranes. Interestingly, we found that the interaction of HSPA5 with negatively charged liposomes promotes an oligomerization process via intermolecular disulfide bonds in which the N-terminus end of the protein plays a critical role.

Stress proteins: the biological functions in virus infection, present and challenges for target-based antiviral drug development.

Stress proteins (SPs) including heat-shock proteins (HSPs), RNA chaperones, and ER associated stress proteins are molecular chaperones essential for cellular homeostasis. The major functions of HSPs include chaperoning misfolded or unfolded polypeptides, protecting cells from toxic stress, and presenting immune and inflammatory cytokines. Regarded as a double-edged sword, HSPs also cooperate with numerous viruses and cancer cells to promote their survival. RNA chaperones are a group of heterogeneous nuclear ribonucleoproteins (hnRNPs), which are essential factors for manipulating both the functions and metabolisms of pre-mRNAs/hnRNAs transcribed by RNA polymerase II. hnRNPs involve in a large number of cellular processes, including chromatin remodelling, transcription regulation, RNP assembly and stabilization, RNA export, virus replication, histone-like nucleoid structuring, and even intracellular immunity. Dysregulation of stress proteins is associated with many human diseases including human cancer, cardiovascular diseases, neurodegenerative diseases (e.g., Parkinson's diseases, Alzheimer disease), stroke and infectious diseases. In this review, we summarized the biologic function of stress proteins, and current progress on their mechanisms related to virus reproduction and diseases caused by virus infections. As SPs also attract a great interest as potential antiviral targets (e.g., COVID-19), we also discuss the present progress and challenges in this area of HSP-based drug development, as well as with compounds already under clinical evaluation.

SARS-CoV-2 host tropism: An in silico analysis of the main cellular factors.

Recent reports have shown that small and big felines could be infected by SARS-CoV-2, while other animals, like swines and mice, are apparently not susceptible to this infection. These findings raise the question of the role of cell factors associated with early stages of the viral infection in host selectivity. The cellular receptor for SARS-CoV-2 is the Angiotensin Converting Enzyme (ACE2). Transmembrane protease serine 2 (TMPRSS2) has been shown to prime the viral spike for its interaction with its receptor. GRP78 has also been proposed as a possible co-receptor. In this study, we used several bioinformatics approaches to bring clues in the interaction of ACE2, TMPRSS2, and GRP78 with SARS-CoV-2. We selected several mammalian hosts that could play a key role in viral spread by acting as secondary hosts (cats, dogs, pigs, mice, and ferrets) and evaluated their predicted permissiveness by in silico analysis. Results showed that ionic pairs (salt bridges, N-O pair, and long-range interactions) produced between ACE2 and the viral spike has an essential function in the host interaction. On the other hand, TMPRSS2 and GRP78 are proteins with high homology in all the evaluated hosts. Thus, these proteins do not seem to play a role in host selectivity, suggesting that other factors may play a role in the non-permissivity in some of these hosts. These proteins represent however interesting cell targets that could be explored in order to control the virus replication in humans and in the intermediary hosts.

GRP78 targeting: Hitting two birds with a stone.

BACKGROUND: Glucose regulating protein 78 (GRP78) is one member of the Heat Shock Protein family of chaperone proteins (HSPA5) found in eukaryotes. It acts as the master of the Unfolded Protein Response (UPR) process in the lumen of the Endoplasmic Reticulum (ER). SCOPE: Under the stress of unfolded proteins, GRP78 binds to the unfolded proteins to prevent misfolding, while under the load of the unfolded protein, it drives the cell to autophagy or apoptosis. Several attempts reported the overexpression of GRP78 on the cell membrane of cancer cells and cells infected with viruses or fungi. MAJOR CONCLUSIONS: Cell-surface GRP78 is used as a cancer cell target in previous studies. Additionally, GRP78 is used as a drug target to stop the progression of cancer cells by different compounds, including peptides, antibodies, and some natural compounds. Additionally, it can be used as a protein target to reduce the infectivity of different viruses, including the pandemic SARS-CoV-2. Besides, GRP78 targeting is used in diagnosis and imaging modalities using radionuclides. GENERAL SIGNIFICANCE: This review summarizes the various attempts that used GRP78 both in therapy (fighting cancer, viral and fungal infections) and diagnosis (imaging).